How well does that Eurail system work? Looks like two adults traveling together could do Germany Luxembourg Belgium france and Ireland for about $900
Rail in Europe is great, but it does come with its cons. Primarily time compared to a bargain airline.
The trains take you to the downtown station, where you want to be.
The discount airlines fly in and out of the farthest out airport with cheapest fees. Then you spend time and money getting downtown. The cheap airlines use Hahn airport for Frankfurt, Hahn is in the middle of no where with no public transportation.
That is why trains are still used in Europe for shorter travel, say Koeln to Munich. One would need to research the options.
Edit - to be clear I would fly from Rome to London.
The trains are great for shorter travel.
I would just target Belgium and Germany (maybe Czech Rep.) for a trip. Brussels to Koeln and Duesseldorf, then down to Munich (mostly high speed), Munich to Nuremburg (high speed), Nuremberg to Bamberg.
Edit 2 - we have bought German rail passes for travel in Germany only. Not so expensive.